Crackling popping in my MM HD 212 130

Two weeks ago a crackling popping sound started in my MM HD 212 130.It gets worse naturally from the 65 to 130 watt settings. I canged the 12Ax7 driver tube to no avail. The Output tubes seem OK. It sounds like a field of light bulbs popping randomly. I cannot play it. Everything works but the noise interferes tremendously. Is it the filter caps? If Steve or anyone can help me it would be much appreciated.

Filter caps are a possibility but by no means a certainty.
It the noise a constant level regardless of volume or Master Volume control settings?
What you describe sounds a lot like "pop-corn noise", which is usually caused by a solid state component (IC, Transistor or Diode).